Method for fabricating a contact on a semiconductor substrate by depositing an aluminum oxide diffusion barrier layer

Abstract

Thin film structures comprising a layer of aluminum and a material having a tendency to interact with aluminum are separated by an intermediate layer of aluminum having a high aluminum oxide content. The intermediate layer prevents said interaction by acting as a diffusion barrier. Preferred embodiments are directed to silicon semiconductor metallization structures, including Schottky barrier contacts, which comprise a bottom layer of tantalum, or other transition metal, or a metal silicide in contact with a silicon substrate, an intermediate layer of aluminum having a high aluminum oxide content and a top layer of aluminum. The intermediate layer functions as a diffusion barrier between aluminum and the metal, metal silicide or silicon. The preferred embodiments of the invention also includes the process for forming such structures preferably comprising: depositing pure tantalum under high vacuum in evaporation apparatus, substituting aluminum for tantalum in the evaporation apparatus and bleeding-in water, air or oxygen to form the aluminum oxide-rich intermediate aluminum layer and then returning to the high vacuum to deposit pure aluminum. The invention is also applicable to FET or CCD structures where a diffusion barrier for aluminum is required.

We claim: 
     
       1. A method for fabricating a contact on a silicon semi-conductor substrate comprising: depositing a transition metal layer upon a portion of said substrate in a vacuum chamber at a low pressure so as to avoid oxidation of said transition metal layer;   depositing an intermediate layer of aluminum having an aluminum oxide content sufficient to provide an effective barrier to the diffusion of aluminum into said transition metal layer upon said transition metal layer; and   depositing an upper layer of aluminum atop said intermediate layer.   
     
     
       2. A method as in claim 1 further comprising the step of: depositing an intermediate layer of a transition metal having a high transition metal oxide content between said transition metal and said intermediate layer of aluminum having an aluminum oxide content.   
     
     
       3. A method as in claim 2 wherein said depositing steps are selected from the group consisting of evaporation and RF sputtering. 
     
     
       4. A method as in claim 1 wherein said upper layer of aluminum is in direct contact with said intermediate layer of aluminum having an aluminum oxide content. 
     
     
       5. A method as in claim 1 wherein said depositing setups are selected from the group consisting of evaporation and RF sputtering. 
     
     
       6. A method as in claim 1 wherein said transition metal is selected from the group consisting of tantalum, zirconium, hafnium, titanium and nickel. 
     
     
       7. A method for fabricating a contact on a silicon semiconductor substrate comprising: evaporating a first transition metal layer upon at least a selected portion of said substrate while maintaining a low pressure in a vacuum chamber so as to avoid oxidation of said transition metal;   evaporating a layer of aluminum upon said first transition metal layer at increased pressure within said chamber so as to deposit an intermediate layer of aluminum having an aluminum oxide content sufficient to provide an effective barrier to the diffusion of aluminum into said transition metal layer atop said first transition metal layer; and   evaporating an upper layer of aluminum at reduced pressure atop said intermediate layer.   
     
     
       8. A method as in claim 7 wherein said transition metal is selected from the group consisting of tantalum, zirconium, hafnium, titanium and nickel. 
     
     
       9. A method as in claim 7 wherein said first transition metal layer is tantalum,   the thickness of said first tantalum layer is around 1000 A, and   the thickness of said intermediate layer of aluminum having a high aluminum oxide content is less than around 1000 A.   
     
     
       10. A method as in claim 7 further comprising the step of: evaporating a second layer of said transition metal atop said first transition metal layer at increased pressure so as to form an intermediate layer of said transition metal having a high transition metal oxide content, said evaporation being done prior to the evaporation of said intermediate layer of aluminum having an aluminum oxide content.   
     
     
       11. A method as in claim 10 wherein said transition metal is tantalum, the thickness of said first tantalum layer is around 1000 A;   the thickness of said intermediate layer of tantalum having a high tantalum oxide content is around 200 A; and   the thickness of said intermediate layer of aluminum having an aluminum oxide content is less than around 1000 A.